This invention relates to the production of electric power generated from the wind. More specifically, the invention relates to the production of electrical power from wind with relatively low wind speed and at relatively low cost.
Wind turbines represent a safe and clean source of power. One of the main problems with generating power from the wind is that it is often difficult to extract significant amounts of power from wind. Additionally, even in areas of relatively high wind it is often the case that using wind power to generate electricity is not cost effective.
In a conventional windmill used for generating electricity it is common to have a large propeller mounted on a tall tower in an area known to have high winds. This limits the use of electrical power generation from wind due to the availability of suitable areas with high winds. When a windmill with this design is used in an area with lower wind speed it often does not produce an adequate amount of electrical power. When this style of windmill is used in lower wind conditions the propeller""s rotational speed is often inadequate or insufficient torque is available for direct input to a large generator, so the use of a high ratio transmission is necessary to increase the input to the generator. Since the single wind turbine is very large it rotates slowly such that the outside edge of the turbine is not rotating too fast. If the outside edge of the turbine is moving too fast then the turbine will be subjected to significant mechanical stress which may lead to failure. In order to prevent excessive stress on the wind turbine, most designs for wind turbines feature some sort of braking system to prevent damage associated with high wind conditions. For example in U.S. Pat. No. 1,533,467, filed Jun. 16, 1921, Sargent uses a spring mechanism to vary the angle of the blades of the propeller. In a very high wind the blades are turned into the wind to reduce their rotational velocity.
Additionally, the single large diameter turbine produces very high torque at relatively low speed. The high torque at low speed must be converted to a lower torque at a higher speed to produce usable power from a conventional generator. Since the torque load is high, a gear system used to couple the single turbine to a generator will be prone to high cost and wear.
Additionally, high loads lead to situations in which rotor blades stall prematurely when insufficient wind is available. To marginally increase generator output using a single wind turbine, the turbine size must increase disproportionately. Increased size in a rotor blade will cause problems with weight, strength of building materials, and vibration. Consequently a substantial amount of energy is lost due to friction, or drag.
In U.S. Pat. No. 2,153,523, filed Mar. 25, 1937, Roberts et al. describe a wind generating turbine in which the generator is driven by two sets of propeller blades. The first set of blades drive an armature. The second set of blades drive the field coils that rotate in the opposite direction to the first set of blades. This prior art does not incorporate any gears between the propeller rotors and the electrical generator. Additionally, the two rotating elements are not mechanically linked. Since the second propeller is located behind the first there is less energy available to it. Consequently, Roberts et al. recommend that the second propeller be larger than that the first so that both propellers extract a similar amount of energy.
It is well known in the art that the high speeds necessary to generate usable electricity from normal wind energy require that the components in the generator rotate much faster than the propeller rotors. Consequently, the design presented by Roberts will not produce power efficiently. Additionally, since this design has no gears it likely has very little friction however it is unlikely that normal winds are strong enough to produce significant amounts of power from this configuration.
In U.S. Pat. No. 4,710,100, filed May 17, 1987, Liang et al. describe the advantages of using relatively small diameter propellers that work in groups to generate electricity instead of using a single larger propeller. Liang correctly points out that the cost of larger turbines is very high in comparison with the cost of a set of smaller turbines capable of covering the swept area. Liang further demonstrates that the gyroscopic torque, blade vibration, inertia and weight are all substantially improved by using a few small turbines for a given swept area instead of one large one. Additionally, a pair of propellers can be arranged such that the gyroscopic torques are equal an opposite. Also, the cost of gears for stepping up the rotational speed of the output shaft is much lower due to the lower torque requirements. These effects all result in a much lighter system. It follows that the tower used to mount this system is also much lighter, simpler and less expensive. Consequently, the tower is also much less expensive. Liang suggests mechanically linking the propellers together, resulting in them all having the same rotational speed. The mechanical output of the combined system is then used to pressurize a flow of water that is used to drive a generator for producing electricity.
In U.S. Pat. No. 5,506,453, filed Dec. 18, 1991, McCombs describes a wind turbine system with a first turbine on one end of a pod and a second turbine on the opposite end of a pod. McCombs takes advantage of gearing to increase the rotational speed of the generator inputs as well as using a generator similar to the generator disclosed by Roberts et al. as explained previously. Unfortunately, disruption of the airflow caused by the first turbine reduces the effectiveness of the second turbine. Due to the design of the generator, it is necessary to either link the two inputs to the generator or care must be taken to ensure that both inputs have roughly equal torque and rotational velocity. Consequently, it is necessary to ensure that both turbines extract the same amount of power from the wind. Unfortunately, disruption of the airflow caused by the first turbine reduces the effectiveness of the second turbine. This may be overcome by increasing the size of the second turbine, using a less efficient first turbine or moving the second turbine so far from the first that the airflow is no longer disrupted. Clearly these solutions will result in either less power output or increased cost.
In a wind farm, a large rotor blade produces large wind shadows, and therefore other nearby wind generators within the wind shadow operate below peak efficiency. Consequently, wind generators must be separated to avoid problems caused by wind shadow.
For the reasons previously stated, today""s wind generators are limited to high wind areas such as hilltops and shorelines. Many more areas have wind that is not as fast as the wind required for a conventional wind turbine.
Clearly, it would be advantageous to produce a practical electrical power generating system that effectively uses a wider range of wind speeds as an energy source.
According to the invention there is provided an electrical generator for converting energy from wind into electrical energy comprising:
a first rotor for converting wind energy into rotational energy and disposed with a first axis of rotation;
a second rotor for converting wind energy into rotational energy disposed with a second axis of rotation different from the first axis of rotation; and
a generator having;
a first field rotor in mechanical communication with the first rotor for receiving rotational energy therefrom, and
a second field rotor in mechanical communication with the second rotor for receiving rotational energy therefrom;
wherein in use rotation of the first rotor in response to wind causes rotation of the first field rotor in a first direction and rotation of the second rotor in response to a wind with approximately same direction and energy causes rotation of the second field rotor in a second opposite direction.
Additionally the invention teaches an electrical generator for converting energy from wind into electrical energy comprising:
a rotor for converting wind energy into rotational energy and disposed with a first axis of rotation;
a generator having;
a first field rotor in mechanical communication with the first rotor for receiving rotational energy therefrom, and
a second field rotor in mechanical communication with the first rotor for receiving rotational energy therefrom;
wherein, in use, rotation of the rotor in response to wind causes rotation of the first field rotor in a first direction and the second field rotor in a second opposite direction.